Narrow-band microcavity waveguides in photonic crystals.

A novel device, formed by a widely spaced periodic array of defects in a photonic bandgap crystal, is studied with the goal of designing a waveguide with a prescribed narrow bandwidth. Tunneling of radiation between the defect sites allows wave propagation along the line of the defects. An analytical study based on the weakly coupled cavity model is performed, and the dispersion relation omega(beta) of the new waveguide is derived. The frequency shift and the band structure of the periodic defect waveguide are linked by an analytic relationship to the distance between the defect sites and therefore can be tuned by varying the latter. Sections of such waveguides can be employed as ultra-narrow-band filters in optical routing devices. Numerical simulations demonstrate the performances of this new device and support the analytical predictions.